1. Field of the Invention
The present invention relates to a compound water meter of the type having main and secondary meter devices and a switch-over valve for controlling switching in and out of the main meter device and, more particularly, is concerned with a compound water meter having an impeller rotatably supported by and between main meter measuring and switch-over valve insets which are connected together to form an inset unit suspended by a cover closing an upper opening of the compound water meter housing.
2. Description of the Prior Art
Compound water meters are used in cases in which the measuring range of a simple meter is not sufficient to cover all throughflows which might occur. These compound water meters include a large water meter as the main meter device, a house water meter as a secondary meter device, and a switch-over valve. The switch-over valve controls the switching in and out of the main meter device, which as a rule, is realized as a Woltmann meter and assumes volume measurement only for relatively large predetermined throughflows in addition to the secondary meter device.
Compound water meters are known in which the switch-over valve is implemented as a weight-loaded hinged flap, as disclosed in U.S. Pat. No. 4,100,800, which upon being completely opened gates the throughflow cross section. The weight-loaded hinged flap swivels in the process about a pivot being laterally offset from the throughflow cross section. The disadvantage of this configuration is that for the pivoting of the hinged flap to occur much volume is required which leads to long and heavy compound water meters.
Furthermore are known compound water meters of the above-cited type, for example from German patent document Nos. DE 37 32 703 A1, DE 37 40 531 A1 or DE 39 24 147 C1. In the case of these meters, the closure member of the switch-over valve is guided translationally on an axle located centrally in the direction of flow, and loaded with a spring which presses it counter to the direction of flow into contact on a valve seat. Starting at a predetermined throughflow quantity, the closure member moves away from the valve seat while overcoming the spring force and is displaced in the direction of flow. Thereby an annular throughflow cross section is enabled. Switch-over valves structured in this way have a smaller space requirement compared to the above-cited prior art but are still rather long, which has a negative effect on the length and weight of the compound water meter.
In addition, a main meter measuring inset of known compound water meters is generally structured such that in its measuring volume an impeller is rotatably supported between two hubs of the main meter measuring inset mounted via webs in the measuring volume. In the hub disposed on the downstream side of the impeller a mechanical pickup of the rotational speed of the impeller is taken, for example from a worm gear pinion, which is transmitted via a shaft to a counter. The employment of hubs on both upstream and downstream side of the impeller to rotatably support the impeller and provision of a mechanical pickup in the downstream hub has a further negative effect on the length and weight of the compound water meter.